guidelines for video delivery over a mobile network. for n excee speed stand such in vid fi limit of...

Copyright Ⓒ 2014 NTT DOCOMO, INC. All Rights Reserved.

Guidelines For Video Delivery Over A Mobile Network

--For efficient video delivery--

Version 1.0

July 1st, 2014

NTT DOCOMO, Inc.


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Contents

Chapter 1. Introduction .......................................................................................................... - 6 -

1.1. Target of this document .............................................................................................. - 6 -

1.2. Structure of this document ........................................................................................ - 6 -

1.3. References ..................................................................................................................... - 7 -

Chapter 2. Unique characteristics of mobile network services and actions taken by

DOCOMO - 8 -

2.1. Data volume in the mobile network by area and time period ............................ - 8 -

2.2. Limit of transmission speeds up to 128 kbps ........................................................ - 9 -

2.3. NTT DOCOMO’s actions to enhance its mobile network .................................. - 10 -

2.3.1. Quad-band LTE (efficient use of 4 spectrum bands) .................................. - 11 -

2.3.2. Installation of additional LTE base stations ............................................... - 12 -

Chapter 3. Image quality experienced by customers using video delivery service ................. - 13 -

3.1. Factors affecting the image quality of video delivery service .......................... - 13 -

3.2. Relationship between encoding conditions and image quality ........................ - 14 -

3.2.1. Relationship between encoding bitrate and image quality ...................... - 15 -

3.2.2. Relationship between image resolution/frame rate and image quality . - 17 -

3.3. Degradation in quality of experience in a congested mobile network ............ - 18 -

Chapter 4. Technological trends in video delivery .......................................................... - 20 -

4.1. High-compression codec technologies .................................................................... - 20 -

4.2. Video streaming technologies .................................................................................. - 23 -

4.2.1. HTTP streaming (pseudo streaming) ............................................................ - 24 -

4.2.2. HTTP adaptive streaming ............................................................................... - 25 -

Chapter 5. DOCOMO-Suggested measures for efficient network utilization ........... - 27 -

5.1. Optimization of content bitrate (image quality) ................................................. - 27 -

5.1.1. Optimization for H.264/AVC ........................................................................... - 27 -

5.1.2. Optimization for H.265/HEVC ........................................................................ - 28 -

5.2. Optimization of delivery bitrate (Quality of Experience) ................................. - 28 -

5.2.1. Video streaming technologies suitable for a mobile environment .......... - 28 -

5.2.2. Time zone-based delivery rate control .......................................................... - 30 -

5.2.3. UI (User Interface) enabling selection of delivery bitrate ........................ - 30 -

5.3. Other optimization measures .................................................................................. - 31 -

5.3.1. Adjustment of still images on web sites ........................................................ - 31 -

Chapter 6. Examples of measures taken for NTT DOCOMO’s video site .................. - 33 -

6.1. Delivery technologies and their usage tendency at “d-Amine Store” ............. - 33 -

6.1.1. Relationship between delivery technologies and image quality .............. - 33 -

6.1.2. DRM license validity period for Download scheme .................................... - 34 -

6.2. UI enabling selection of delivery bitrate .............................................................. - 34 -


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6.2.1. Video selection screen ....................................................................................... - 35 -

6.2.2. Image quality selection during playback ...................................................... - 35 -

6.3. Adjustment of still images on web sites ............................................................... - 35 -

6.3.1. Resizing for optimal resolution ....................................................................... - 35 -

6.3.2. Volume reduction (optimization) .................................................................... - 36 -

6.3.3. Utilization of browser cache ............................................................................ - 36 -

6.4. Notices for users ......................................................................................................... - 36 -

6.5. Video specifications at “d anime store” ................................................................. - 38 -

6.5.1. File specifications for HTTP streaming/Download technologies ............. - 38 -

6.5.2. File specifications for HLS technology .................................................................. - 40 -

6.6. 【Information】Introduction of tools ........................................................................ - 41 -


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About trademarks

· All the names of the companies, products, and services that are mentioned in this

document are trade names, trademarks, or registered trademarks of their respective

owners.

· This document does not specifically indicate any copyrights, or trademarks or

registered trademarks.


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Revision history

Version Section Type Revisions

1.0 ― First version


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Chapter 1. Introduction

This document describes ways of providing video content over a mobile network aimed

at providing comfortable video viewing experience for users. For comfortable video

viewing experience, it is important to enable users to watch high-resolution video that

runs smoothly without interruptions. However, the use of excessively high bitrates

compared with the forwarding bandwidth that the network can provide may cause video

images to skip or to be delayed, and this may result in deterioration in the service

quality experienced by users. Therefore, it is important, especially in a mobile network,

to maintain a suitable balance in the quality and size of images in video delivery.

While some measures are available to improve the quality of experience, the focus of

this document is placed on those that can be used to optimize content bit rate and

delivery bitrate. The first part of this document presents the fact that even for the same

video, its data size varies depending on the compression measures used, showing some

examples. The second part introduces some background information of a mobile

network and its varying traffic volumes according to the time of day, and then moves on

to discuss specific measures to control image quality based on the time of day. The third

part focuses on HTTP adaptive streaming technology, which can provide smooth and

seamless video streaming and efficiently utilize network resources in a mobile

environment.

The use of measures introduced in this document will help achieve efficient video

delivery. In addition to achieving comfortable video viewing experience to users, this

will generate circumferential benefits through the reduction of their traffic volumes in

the network. Efficient use of the finite resources in a mobile network will not only allow

users to watch video comfortably but also enable others around them to use the network

comfortably through suitable allocation of network resources. If your company is

currently providing or planning to provide video content, this document will serve as a

useful guide for achieving video delivery.

1.1. Target of this document

This document was written with video content providers in mind and, therefore, it

presumes that the reader has a basic knowledge of video delivery.

1.2. Structure of this document


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Chapter 2 of this document explains some unique characteristics of a mobile network.

Chapter 3 describes schemes for image quality evaluation. Chapter 4 explains

technological trends in video delivery. The background information provided in

Chapters 2, 3, and 4 will help readers understand the effectiveness of specific measures

introduced in Chapter 5. Those who are more interested in understanding specific

measures and implementation methods can directly start reading Chapter 5 before the

preceding Chapters 2, 3, and 4. Chapter 5 provides a systematic description of specific

measures. Lastly, Chapter 6 presents some measures actually implemented by NTT

DOCOMO as reference information. These examples are useful to have a better

understanding of the details described in this document.

Please note that this document does not cover descriptions of server applications used

for video delivery or terminal apps for video reception. This is due to an assumption that

server applications and terminal apps that can use the technologies described in this

document will be addressed by content providers engaged in video delivery.

1.3. References

[1] F. Dobrian, V. Sekar, A. Awan, I. Stoica, D. A. Joseph, A.Ganjam, J. Zhan, and H.

Zhang, "Understanding the impact of video quality on user engagement," Proc. of ACM

SIGCOMM'11, pp. 362-373, Aug.2011.

[2] ITU-T H.265 | ISO/IEC 23008-2 High Efficiency Video Coding

[3] ITU-T H.264 | ISO/IEC 14496-10 Advanced video coding for generic audiovisual

services

[4] Jun Okamoto and Takanori Hayashi, “Latest trends in image media quality

assessment technologies,” IEICE Fundamentals Review, Vol.6, No.4, pp.276-284, April

2013.(in Japanese)

[5] ITU-T Recommendation P.910, “Subjective video quality assessment methods for

multimedia applications,” April 2008.

[6] ISO/IEC 23009-1 Information technology – Dynamic adaptive streaming over

HTTP(DASH) – Part1: Media presentation description and segment formats


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Chapter 2. Unique characteristics of mobile network services

and actions taken by DOCOMO

2.1. Data volume in the mobile network by area and time period

Characteristics of a mobile network include varying peak hours depending on the

characteristics of areas* (see Figure 2-1 below). As of December 2013, the level of

congestion in the DOCOMO network peaks from 10 p.m. to 11 p.m. This is based on the

total volume of data generated by NTT DOCOMO’s Xi (LTE) service subscribers going

through the sp mode center. A closer analysis of smaller areas reveals that the peak

time varies in different areas. The peak time is from 12 noon to 1 p.m. in an area

covering a business district; from 7 a.m. to 8 a.m. and 6 p.m. to 7 p.m. at an urban

terminal station area; and from 12 midnight to 1 a.m. in a residential area. This shows

that each area experiences congestion in a different time zone. A failure to use an

optimal bitrate for video delivery in respective areas and time zones will increase the

risk of causing more intermissions and slowdowns in video. This makes users feel stress

during video viewing (lowering the quality of experience for users). Therefore, in order

to improve the quality of user experience, it is important to dynamically change the

delivery bitrate to optimize video delivery in accordance with the degree of congestion in

the network, using measures such as those hereinafter described.

*The “area” mentioned here is defined as an area covered by one or more base

stations.

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Table 2-1 Summary of major Xi Packet Flat-rate services (currently available)

Xi Packet Flat-rate

Services

Max data volume for a

normal transmission speed

Requirement for

removing the 128kbps

cap

Xi Pake-hodai Light 3GB/month Payment of extra charges

for every 2GB data usageXi Pake-hodai Flat

7GB/month Xi Pake-hodai for iPhone

*For details of Xi Packet Flat-rate Servcies, please refer to NTT DOCOMO’s web page

(URL: https://www.nttdocomo.co.jp/charge/packet/index.html)

Table 2-1 Summary of major Packet Packs in new billing plans

（available from June 1, 2014）

Packet Pack Max data volume for a normal

transmission speed

Requirement for removing

the 128kbps cap

Raku-Raku Pack 200MB/month

Payment of extra charges

for every 1GB data usage

Data S Pack 2GB/month

Data M Pack 5GB/month

Share Pack 10 10GB/month (per group)

Share Pack 15 15GB/ month (per group)



*For details of the new billing plans “Kake-hodai & Pake-aeru,” which will help families

save money, please refer to NTT DOCOMO’s web page.

(URL:https://www.nttdocomo.co.jp/charge/new_plan/index.html?icid=CRP_TOP_main

PR_new_plan#charge)

2.3. NTT DOCOMO’s actions to enhance its mobile network

NTT DOCOMO is enhancing its mobile network by efficiently using four spectrum

bands (quad-band LTE) and installing more LTE base stations to support growing data

volume.

In addition to the actions above taken by NTT DOCOMO, content providers can also

play a role in making the users’ video watching experience much more comfortable by

using measures that will be described in Chapter 5 for video delivery. For actions taken

by NTT DOCOMO to enhance its mobile network, please refer to NTT DOCOMO’s web

page (URL: https://www.nttdocomo.co.jp/xi/index.html)


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2.3.1. Quad-band LTE (efficient use of 4 spectrum bands) NTT DOCOMO’s LTE “Xi” service efficiently utilizes the four spectrum bands - 1.7GHz,

1.5GHz, 800MHz, and 2GHz- in order to further enhance its mobile network.

The 2GHz and 800MHz bands have been used to provide “coverage” and the 1.5GHz

band to provide “speed.” In September 2013, the 1.7 GHz band was added to NTT

DOCOMO’s 3 operation bands mentioned above to launch its “quad-band LTE”

operation.

Figure 2-2 Image of quad-band LTE

Efficient use of 4 spectrum bands

In Tokyo, Nagoya, Osaka, more than double the spectrum In preparation 3G band LTE band

Platinum band

Platinum band

Before 19 September, 2013 20 September, 2013 April 2014


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2.3.2. Installation of additional LTE base stations NTT DOCOMO is installing more LTE base stations to expand its LTE “Xi” areas so

that connections will be available anytime, anywhere. The number of its LTE base

stations will be increased 1.7 times over the fiscal year 2014 (from approx. 55,300 at the

end of FY 2013 to approx. 95,300 at the end of FY 2014) and the number of 100Mpbs

base stations more than 10 times (from approx. 3,500 to 40,000 during the same period

as above) for further enhancement of its LTE network.

Figure 2-3 LTE Xi base station installation plan

LTE base stations to be more significantly increased

24,400

95,300

End of FY2013End of FY2012 End of FY2014 (target)

100Mbps

base stations

40,000 3,500

55,300

1.7 times increase of LTE base stations

10 times increase of 100Mpbs base

t ti


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Chapter 3. Image quality experienced by customers using

video delivery service

3.1. Factors affecting the image quality of video delivery service This section describes some factors that affect the quality of images experienced by

users (Quality of Experience) in video delivery service.

Figure 3-1 shows elements that constitute video delivery service using a mobile network

as well as major factors that affect the video image quality. Video data is encoded into a

format suitable for transmission over the network and stored in the delivery server of a

content provider. NTT DOCOMO’s network receives video data over the Internet, etc.

and forwards it via a radio link such as an LTE network to smartphones, tablets, and

other video viewing terminals. The terminal that receives the video data decodes the

data into images that are to be displayed on its screen.

The image quality of video delivery service is affected by different elements that

constitute video delivery service. Major factors that affect the image quality of video

delivery service are generally classified as follows:

(1) Image encoding conditions;

(2) Throughput characteristics of transmission of encoded data over a mobile network;

(3) Performance of the video viewing terminal.

First, (1) Image encoding conditions for video delivery include the following.

・Coding scheme

・Encoding bitrate

When the bitrate is set low, it results in lack of sharpness (blurring) or mosaic-like

distortions (, which is called “block-noise”) in images.

・Image resolution

When the image resolution is low, it reduces the definition of images.

・Frame rate

When the frame rate is low, it reduces the smoothness of motions, resulting in

flickering and jerky images.

Second, when (2) the throughput of the mobile network is too low, the download of video

data cannot catch up with the playback of video on the terminal. As a result, the

playback is halted until a certain amount of video data are stored again in the terminal

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the relationship between encoding bitrate and image quality

3.2.2. Relationship between image resolution/frame rate and image quality

An increasing number of content providers are handling high-resolution images such as

those for high-definition television (HDTV) in order to provide users with

high-resolution video delivery service. The current mobile network environment,

however, is not always fully prepared to ensure the bandwidth sufficient for delivery of

HDTV-class video. This makes necessary to select a suitable image resolution and frame

rate in order to achieve higher video quality with a smaller bandwidth. Coding with a

low image resolution can yield high quality image in a low bandwidth. This relationship

is shown in Figure 3-4. In an example illustrated in Figure 3-4, the encoder using the

bitrates B1, B2, and B3 achieves their optimal video image quality for the image

resolutions of 320×240, 640×480, and 1280×720, respectively. When an encoding bitrate

lower than a level of 100 to 200kbps is used, reducing the frame rate is effective from

the standpoint of maintaining the image quality. However, reducing the frame rate in

fast-motion video such as of a sport scene will make the flickering and jerky parts more

noticeable. Degradation in the quality of experience can be minimized for content like

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Chapter 4. Technological trends in video delivery

4.1. High-compression codec technologies

The latest video compression standard HEVC or officially called “ITU-T H.265 |

ISO/IEC 23008-2 High Efficiency Video Coding[2]” was approved by the ITU in January

2013. HEVC is an all-purpose standard designed to address a wide range of applications

from video on small screens of mobile devices to high-definition video with HD

resolution of 4K, 8K or higher. The HEVC standard was developed to double the

compression rate compared with the conventional H.264/AVC standard[3].

First, this section describes the terms “Profile,” “Level,” and “Tier,” which denote the

playback capability of an H.265/HEVC decoder.

The current H.265/HEVC standard defines the following three Profiles:

-Main Profile;

-Main 10 Profile;

-Main Still Picture Profile.

Both of Main Profile and Main 10 Profile are profiles for video compression, using

different bit depths to express one pixel. Main Profile only supports video with a depth

of 8 bits per pixel while Main 10 Profile also supports 10 bits per pixel in addition to 8

bits per pixel. Except for bit depth coding, the both Profiles use common technical

elements for coding. Both of them only support the chroma subsampling format of 4:2:0

(in which the amount of information on color difference is a quarter of that of

brightness), which is for consumer applications. An extension of the H.265/HEVC

standard called RExt is being standardized to support formats with a large color

difference, such as 4:2:2 and 4:4:4, which are mainly used for material transmission in

broadcasting stations. HEVC RExt also aims to support video with a bit depth higher

than 10bits per pixel. Thus, HEVC RExt is a standard mainly targeted at compression

and transmission of high-definition video, such as digital cinema and material

transmission. As for interlaced video, Main Profile and Main 10 Profile can handle this

type of video . However they haven’t introduced any coding tools specialized for

interlaced video and currently only use flags to mark it in the stream. In actual

processing, interlaced video is encoded as progressive video with its top and bottom

fields separated.

Next part discusses the Level and Tier. There are 13 Levels from 1 to 6.2, each of which

mainly specifies the maximum resolution and frame rate. The Tier, on the other hand, is


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divided into two, the main Tier and the high Tier, each of which specifies the maximum

bitrate at each level. H.264/AVC does not have a concept of Tier but specifies

everything including the maximum resolution, frame rate, and bitrate, using the Level

only. However, this makes it difficult to address a case where only the bitrate should be

restricted. H.265/HEVC, which has newly introduced the concept of Tier, is able to

specify the restriction on the resolution, frame rate, and bitrate, separately. Table 4-1

below shows a list of major resolutions, and Levels and Tiers.

Table 4-1 List of main resolutions, Levels, and Tiers

Main

Levels

Examples of maximum

resolution and frame rate

Maximum video bitrate [kbps]

Main Tier High Tier

1 QCIF 15fps 128 －

2 CIF 30fps 1,500 －

3 QHD(960x540) 30fps 6,000 －

4 2Kx1080(2048x1080)

30fps

12,000 30,000

5 4096x2160 30fps 25,000 100,000

6 8192x4096 30fps 60,000 240,000

6.2 8192x4096 120fps 240,000 800,000

Listed below are specific examples of coding technologies used in H.265/HEVC.

- Block partitioning

- Inter and intra prediction

- Orthogonal transform

- Variable-length coding

- In-loop filter

As is the case with major conventional coding standards, H.265/HEVC adopts a

compression scheme based on a combination of motion compensating prediction and

orthogonal transform. H.265/HEVC doubles the compression performance of H.264/AVC

by accumulating improvements in individual coding tools. However, H.265/HEVC has

no compatibility with conventional standards. Furthermore, its complexity gradually

adds more processing load, especially at the time of compression. To cope with this,

researchers and developers are working on to develop an H.265/HEVC encoder capable

of high-speed operation.

As shown in Figure 4-1, a hierarchical block portioning structure (Coding Tree Unit;

CTU) is introduced to H.265/HEVC to enable efficient coding of video images in widely

varying levels of resolution. Each block in the CTU is further split into subdivisions

called PUs (Prediction Units). By combining all these blocks, a wide variety of blocks

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- 23 -

been excluded and is not available for H.265/HEVC in consideration of the progress of

device performance in recent years.

For an in-loop filter, the deblocking filter for block noise reduction and the Sample

Adaptive Offset (SAO) for ringing and pixel value shift control have been introduced.

These have contributed to achieving a reduction of coding distortion.

Table 4-2 provides a comparative summary of coding tools between H.265/HEVC and

H.264/AVC.

Table 4-2 Comparative summary of coding tools of H.264/AVC and H.265/HEVC

Coding tool H.264/AVC (High Profile) H.265/HEVC

Intra prediction 4x4 block: 9 modes

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35 modes for 4x4 to 64x64

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4.2. Video streaming technologies

Video streaming technologies are available for delivery of video content over a network .

Video streaming technologies are mainly divided into two groups depending on the

protocols they use: HTTP and non-HTTP (RTSP：Real-Time Streaming Protocol, etc.).

Video delivery services today use HTTP-based streaming technologies. This is because


- 24 -

the HTTP protocol has excellent conformity with standard web servers and existing

server systems in that it can make use of HTTP cache. HTTP is also highly compatible

with user systems in that it can transparently go through firewalls and NATs. Most

well-known HTTP-based streaming technologies are HTTP streaming and HTTP

adaptive streaming.

In video delivery, the quality of experience of users is affected by the quality of video

(resolution, frame rate, etc.) and the smoothness of playback. Raising the quality of

video increases the amount of data (bitrate) flowing over the network. The more the

video bitrate exceeds the transfer speed, the more frequently video playback will be

interrupted. In this manner, video quality and playback smoothness are in the

relationship of trade-off. Especially in a mobile environment, characterized by unstable

and highly fluctuating transfer speed, our challenge is how to ensure playback

smoothness. HTTP adaptive streaming is aimed at mitigating such trade-off.

4.2.1. HTTP streaming (pseudo streaming) This is the most widely utilized streaming technology in video delivery service. In HTTP

streaming, when the user starts video playback, it triggers the download of a selected

video file from the web server. A video playback application (web browser or media

browser) performs sequential playback of the buffered video data in parallel with the

download of the video file.

The bitrate of the downloaded video data is fixed from the start to the end of its

playback. When the bitrate of the specified video data is high, it takes a long time until

the start of playback due to a large amount of data to be buffered. Although the amount

of data in the buffer is reduced as the playback proceeds, the playback will be

interrupted if the buffer is exhausted. To restart the playback, it is necessary to obtain

buffered data once again. If the user cancels the playback at this point, the data not yet

played back will be discarded. This means that the resources of the server and network

used for the download will be wasted.

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- 27 -

Chapter 5. DOCOMO-Suggested measures for efficient

network utilization

This chapter introduces some recommended measures that should be considered for

adoption to achieve efficient use of a mobile network for video delivery.

5.1. Optimization of content bitrate (image quality)

5.1.1. Optimization for H.264/AVC Table 5-1 shows a general relationship between the video image quality and the

DOCOMO-suggested image resolution and encoding bitrate for the H.264/AVC coding

technology. The “image quality” in the table means the quality of images experienced by

the user (quality of experience) who watches the video. The image quality in the table is

quantified based on the subjective perception (subjective quality) of humans users, such

as “clear image,” “smooth video,” and “image quality degradation perceptible but not

annoying.”2 Table 5-1 shows a result of a case using Main Profile as the profile, a frame

rate of 30fps, and a random access interval of approximately one second (32 frames). As

described earlier, when the encoding bitrate becomes low, the use of low image

resolution helps reduce image quality degradation. The table shows a sample case in

which the image resolutions are changed corresponding to the encoding bitrates.

Table 5-1 Relationship between image quality and DOCOMO-suggested image

resolution/encoding bitrate (in case of H.264/AVC)

Coding scheme：

H.264/AVC Image quality

Low Middle High

Suggested image

resolution

360p-equivalent

(640×360)

360p-equivalent

(640×360)

720p-equivalent

(1280×720)

Suggested video

encoding bitrate

S: approx. 350kbps

T/P: approx. 400kbps

S: approx.700kbps


S: approx. 1.4Mbps

T/P: approx. 1.6Mbps

2The image quality was determined based on the results of evaluation conducted using the ACR Method (Absolute Category Rating Method), which is an evaluation method adopted as an international standard. Specifically, the quality of images of different types of content were evaluated. The suggested conditions for High, Middle, and Low image quality levels are derived from the content which showed average quality characteristics and evaluated to have ratings of 4, 3, and 2 respectively on the MOS (Mean Opinion Score) scale. For evaluation methods quantifying subjective image quality, please refer to the references [4] and [5], etc.


- 28 -

* S stands for Smartphones: evaluation results from video viewing on 4.7-inch smartphones.

T/P stands for Tablets and PCs: evaluation results from video viewing on 15.5-inch notebook PCs.

* The values of the suggested video encoding bitrates are subject to change.

5.1.2. Optimization for H.265/HEVC

An effective measure to achieve high image quality at a lower encoding bitrate than

that of H.264/AVC is to use a coding scheme with a high compression capability. The

latest H.265/HEVC coding scheme discussed in Chapter 4 is said to almost double the

compression efficiency compared to H.264/AVC. Therefore, H.265/HEVC is expected to

be widely utilized in the mobile video delivery market in the future. Table 5-2 shows a

general relationship between image quality and suggested image resolutions and

encoding bitrates for the current H.265/HEVC coding technology. The table shows a

result of study of a case that uses Main Profile as the profile, a frame rate of 30fps, and

a random access interval of approximately one second (32 frames). Future

improvements in H.265/HEVC implementation technology are expected to achieve even

higher compression levels.

Table 5-2 Relationship between image quality and DOCOMO-Suggested image

resolution/encoding bitrate (in case of H.265)

Coding scheme:

H.265/HEVC Image quality

Low Middle High

Suggested image

resolution

360p-equivalent

(640×360)

360p-equivalent

(640×360)

720p-equivalent

(1280×720)

Suggested video

encoding bitrate

S: approx. 200kbps


S: approx.350kbps


S: approx. 700kbps


* S stands for Smartphones: evaluation results from video viewing on 4.7-inch smartphones.

T/P stands for Tablets and PCs: evaluation results from video viewing on 15.5-inch notebook PCs.

* The values of the suggested video encoding bitrates are subject to change.

* In H.265/HEVC, when a high image resolution is used, coding may take a long time.

5.2. Optimization of delivery bitrate (Quality of Experience)

5.2.1. Video streaming technologies suitable for a mobile environment Table 5-3 shows the status of support on Android and iOS platforms for the streaming

technologies discussed in Section 4.2. HTTP Adaptive Streaming has multiple

technologies. Although they share the same basic concept of switching content files

according to the state of network, they adopt different file formats. MPEG-DASH

(Dynamic Adaptive Streaming over HTTP)[6] is an ISO/IEC standard and is officially

supported on Android4.4 and higher. HLS (HTTP Live Streaming) is a proprietary


- 29 -

technology of Apple Inc., although it is supported on both Android and iOS platforms.

These two HTTP Adaptive Streaming technologies and HTTP streaming are the three

technology options for video delivery for mobile devices. (As stated in Section 4.2, in

light of a mobile environment, the adoption of HTTP Adaptive Streaming (MPEG-DASH

or HLS) is expected to improve user experience.)

This section describes DOCOMO-suggested operation methods for each of the HTTP

Streaming and HTTP Adaptive Streaming technologies in a mobile environment.

Table 5-1 HTTP-based streaming technologies

Technology Specified

By

Support on Android

(*1)

Support on

iOS

HTTP streaming － Supported Supported

HTTP

adaptive

streaming

MPEG-DASH ISO/IEC Android 4.4 and

higher (*2)

Not supported

HLS Apple Android 4.0 and

higher

Supported

Smooth Streaming Microsoft Not supported Not supported

HTTP Dynamic

Streaming

Adobe Not supported Not supported

(*1) The support status is based on a standard Android implementation. For the support

status on smartphones, please refer to products’ specifications.

(*2) Android 4.4 provides a video playback API, which will be necessary to support

MPEG-DASH. The use of MPEG-DASH in video delivery requires implementation of

MPD (Media Presentation Description) file analysis and processing of adaptive

streaming logic using the above-mentioned video playback API on the video playback

application.

5.2.1.1. HTTP adaptive streaming

In the ever-changing state of the mobile communication environment, it is suggested

that HTTP Adaptive Streaming technology be adopted for its ability to provide smooth

and uninterrupted video streaming and effectively utilize network resources. While

HLS and MPEG-DASH are supported on Android OS and iOS, it is requested that

which technology to choose be determined based on whether it is supported by the

target Operating System(s) in video delivery, the content generation tools used, and the

delivery server.

To take advantage of the benefits of Adaptive Streaming technology, it is suggested that

a set of three video stream files in three different bitrates be prepared (in case of HLS,


- 30 -

four files(bitrates) because a file of an audio-only stream is also included). While the

relationship between image resolution and bitrate was explained in Section 5.1., it is

requested that the image resolution level in each stream be adjusted with some margins

added to lower and higher rates to make a wider range of bitrate available. As a

reference, the bitrates used in “d anime store” are shown in Section 6.5.

(Note) DOCOMO’s 2014 summer models do not support HTTP Adaptive Streaming

using video data encoded with H.265/HEVC. Therefore, it is requested that any data

using HTTP Adaptive Streaming be encoded with H.264/AVC.

5.2.1.2. HTTP streaming (pseudo streaming)

For video delivery using HTTP streaming technology, it is suggested that content be

made available at several different bitrates and image resolutions to allow users to

choose the image quality they prefer according to the states of their network and usage.

Please refer to Section 5.1 for the relationship between image resolution and bitrate.

Please refer to Section 6.5 for the operation parameters used in DOCOMO’s d anime

store.

5.2.1.3. Download scheme

The Download scheme is highly effective to enable users to comfortably watch video in a

mobile environment. Users can experience stress-free playback when they are on the

road and in an unstable network environment by downloading video data in a stable

network environment in advance.

5.2.2. Time zone-based delivery rate control In Chapter 3, a drastic degradation of image quality resulting from video stall was

explained. This problem occurs in a congested mobile network even when the encoding

bitrate is raised to improve image quality. In order to avoid such degradation, it will be

effective to perform the following delivery rate control after preparing data sets of the

same video in multiple encoding bitrates. In doing so, please use the peak time zones in

Section 2.1 and suggested encoding bitrates in Section 5.1 as reference.

1. Choose video data encoded in a low bitrate for a time zone where a mobile network

is congested

2. Do not use an unnecessarily high coding bitrate for access from a mobile network

even in a time zone where the mobile network is not congested.

5.2.3. UI (User Interface) enabling selection of delivery bitrate To enable users to smoothly change bitrate according to their network state even in the

middle of playback is one of the simple and effective means to improve quality of


- 31 -

experience of users. This approach mitigates users’ dissatisfaction because they are

given power to make a decision during video viewing as to which to prioritize, image

quality or smooth playback.

The above-mentioned measure is suggested to be used in fixed –rate video delivery such

as HTTP streaming and progressive download.

For an example of how to operate delivery bitrate selection and switching functions at d

anime store , please refer to Section 6.2.

5.3. Other optimization measures

This section describes other suggested measures not covered in the previous sections.

5.3.1. Adjustment of still images on web sites In video delivery service, still images on the web sites to introduce video have the

second-largest volume of data following video images themselves. Although the use of

rich still images is effective in introducing video, slow browsing caused by “heavy” web

sites is a serious issue that can prompt users to cancel services. For the use of still

images on web sites, the following are four generally-known approaches to be taken. It

is strongly requested to consider their introduction in combination with your video

delivery schemes to improve quality of experience perceived by users visiting web sites.

5.3.1.1. Resizing for optimal resolution One still image is used in various sizes in web sites. When only the visual quality of

image is taken into consideration, generating a reduced version of a big file will suffice.

From the standpoint of disk capacity, however, maintaining multiple sizes of one still

image may not be always preferred. On the other hand, sending an image in an

appropriate size greatly reduces the volume of data. Data volume reduction leads not

only to shorter transfer time but also to faster and smoother drawing processing on

smartphones. This improves the quality of experience of users.

5.3.1.2. Image volume reduction (optimization) One of the effective measures well known since the feature-phone age is the utilization

of image volume reduction (optimization) tools. These tools can reduce the volume of

images by modifying them to an extent difficult to recognize with human eyes. Data

compression methods used by tools include increasing compression ratio in JPEG, use of

PNG24 or PNG8 in PNG, and deletion of header information such as Exif information.


- 32 -

5.3.1.3. Utilization of browser cache Utilizing browser cache, known as a measure for faster web browsing, is effective for

images and large-sized JavaScript/CSS files.

Setting cache control of the browser on a web server used for delivery of images enables

the same images to be displayed when users open the web page again. This is done

without the need for transfer (or with a request with an if-modified-since header) or

download of images.

5.3.1.4. Delayed image loading

In web pages, images are used even outside the display area. A mechanism to delay

loading of those images until the time they enter the display area can shorten the

loading time required to complete a screen transition.

There are some plugins publicly available (e.g., Lazy Load Plugin for jQuery), which can

be used to facilitate the introduction of the above-mentioned mechanism and to improve

the quality of the experience for users.


- 33 -

Chapter 6. Examples of measures taken for NTT

DOCOMO’s video site

This chapter provides specific examples of how the measures such as those described in

Chapter 5 have been implemented by NTT DOCOMO to utilize its network efficiently.

6.1. Delivery technologies and their usage tendency at “d-Amine Store”

In accordance with the description in Section 5.2, “d anime store” (DOCOMO’s anime

store) offers two video delivery formats: one for Android and the other for iOS. HTTP

streaming and Download are offered for Android and HLS and Download for iOS. In

addition, the Store offers three image quality levels.

6.1.1. Relationship between delivery technologies and image quality In general, anime users ask for high quality images. At d anime store, however, some

different tendency has been observed among its users. Table 6-1 shows usage ratios for

different image quality levels at d anime store. According to Table 6-1, in case of 3G/LTE,

more users choose the image quality that ensures stable playback. In case of Wi-Fi,

which secures sufficient throughput, they give greater importance to higher image

quality. The data shown in this table indicate that users choose the delivery scheme and

image quality the most suitable to their environment. It also shows that they are

actively utilizing Wi-Fi to view high-quality video.


- 34 -

Table 6-1 Ratio of number of playback times for each usage type

(d anime store, second half of 2013)

Ratio of number of playback

times

Image quality

Total Normal Good Excellent

HTTP

streaming

3G/LTE Approx.

30%

Approx.

20%

Less than

10%

Approx.

40%

Wi-Fi Less than

10%

Approx.

10%

Approx.

20%

Approx.

30%

Download

3G/LTE Approx.

10%

Less than

10%

Less than

10%

Approx.

10%

Wi-Fi Less than

10%

Less than

10%

Approx.

10%

Approx.

10%

Total Approx.

40%

Approx.

30%

Approx.

30% 100%

(Note) Totals may not add up due to rounding.

6.1.2. DRM license validity period for Download scheme For Download, d anime store issues a DRM license valid for 48 hours from the time of

download. This service design enables the user to play video downloaded on a previous

day without generating any further communication. In addition, even after 48 hours

from the download, the user can play the downloaded video only by reacquiring their

DRM license file. This makes the user feel secure in using the service even when their

network environment cannot offer sufficient throughput for video delivery.

6.2. UI enabling selection of delivery bitrate

At d anime store, the user is able to select the delivery bitrate on two screens as shown

in Figure 6-1.

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- 36 -

6.3.2. Volume reduction (optimization) At its service launch, d anime store was using PNG24. After confirming that visual

degradation was limited with PNG8, the store has been using a tool mainly based on

PNG8 compression to perform optimization. By means of the tool, the data volume of

the TOP page has been compressed to one-third of its original volume.

6.3.3. Utilization of browser cache “d anime Store” sets the cache period of images to a relatively longer time so that the

cache is still effective when the user revisits after several days.

6.4. Notices for users

As mentioned in Section 6.1, the quality of experience of users can be improved by

providing video using the delivery scheme and the bitrate suitable to the specific

network environment available for each user. In addition, it is necessary to encourage

users to be conscious of the suitability of the delivery scheme and the bitrate to their

network environment in order to promote measures to improve the quality of experience.

Certain means such as a notice on a web site will be effective to make more users aware

of such measures. Figure 6-2 shows a notice given for that purpose at d anime store as

an example.

The mechanism explained in Section 2.2 has made regular video viewers sensitive to

data volume. Therefore, they are actively utilizing Wi-Fi and selecting image quality.

This is why d anime store provides information on Wi-Fi utilization in the notice shown

in Figure 6-2.


- 37 -

Figure 6-2 A notice introducing measures for comfortable video viewing (d anime store)

Change of communication speeds for Xi

If you are subscribed to a “Packet Flat- rate Service for Xi,”, a 128-kbps cap is imposed on the your communication speed for the

rest of the month when the volume of data used in the current month exceeds a certain threshold (3GB, 7GB).

If the speed is reduced to 128 kbps, you may find it difficult to view video properly. Therefore, we propose certain measures to

enable you to avoid such communication speed change and enjoy your comfortable Anime Store experience.

--Use different lines at different times--

1. Utilize wireless LAN (Wi-Fi) at home.

You can download the episodes of anime you want to view all together via wireless LAN! You can view them without doing

anything special within 48 hours after the download. Even after 48 hours, what you need is only to confirm the license.

2. Utilize docomo Wi-Fi outdoors

docomo Wi-Fi is available at over 70,000 locations, including train stations, airports, coffee shops, fast food restaurants, family

restaurants, and convenience stores. Start now and use WiFi for free forever! You are recommended to apply now!

http://www.nttdocomo.co.jp/info/news_release/2012/08/22_00.html

3. Utilize “Normal” mode when using the mobile phone line (Xi、3G).

With the “Normal” mode, you can view approximately 180 episodes before the data volume reaches 7GB.

--Examples--

・First, you download 10 episodes or so at home or via docomo Wi-Fi.

・Within 48 hours after the download, you view them without doing anything special.

・After 48 hours, only you have to do is license authentication via the mobile phone.

・As you view more of the downloaded episodes, you download another 10 episodes.

・Only for the episodes you haven’t downloaded, you watch them in the “Normal” mode over Xi or 3G.

--Estimated data volume--

“Excellent” (data volume/episode:300MB, 3GB: 10 episodes, 7GB: 24 episodes)

“Good” (data volume/episode:100MB, 3GB: 31 episodes, 7GB: 72 episodes)

“Normal” (data volume/episode: 40MB、3GB:77 episodes, 7GB: 179 episodes)

(Note) The runtime of one episode: approx. 30 minutes. Assumptions: Normal=40MB, Good=100MB, Excellent＝300MB.

--Packet Flat-rate Service for Xi--

For details, please visit DOCOMO web page shown below.

http://www.nttdocomo.co.jp/charge/packet/

--If you want to know your current data usage--

Data volume notice service

http://www.nttdocomo.co.jp/charge/online/notification_service/about/index.html

-->You will receive a notice when your data usage in the current month has reached［2GB, 3GB］or［6GB、7GB］.

MyDocomo

http://www.nttdocomo.co.jp/charge/online/data_traffic/

-->By logging in with your docomo ID, you can see your accurate data usage status.

Data Volume Verification App

http://www.nttdocomo.co.jp/charge/online/data_app/

-->This app enables you to check an estimate of your packet data volume.


- 38 -

6.5. Video specifications at “d anime store”

6.5.1. File specifications for HTTP streaming/Download technologies

“d anime store” is NTT DOCOMO’s video delivery service launched in July 2012.

This service is available for NTT DOCOMO’s Android terminals (DRM-capable models)

released in and after November, 2011. The video specifications for the Store have been

determined based on the specifications supported in playback on these terminal models

in accordance with the concepts shown in Table 6-2.

.

Table 6-2 Image quality concepts of d anime store

Image quality Concept

Normal This is the image quality that responds to the needs of users who want

to watch video even if its image quality is not entirely satisfactory

while on the move or in any other situations difficult to get stable

throughput in a LTE/3G environment.

Good This is the image quality that satisfies users who watch anime video

in a stationary position in a LTE/3G environment.

Excellent This is the image quality that provides users with the highest level of

satisfaction through a video-viewing terminal in a stable network

environment via WiFi, etc.

Based on the concepts above and the characteristics of anime content, d anime store

adopts parameter specifications different from those shown in 5.1.1. Specifically, the

Store uses different frame rates so that they can make the best use of limited bitrates to

realize “excellent images.”


- 39 -

Table 6-3 Video specifications for H.264/AVC (d anime Store)

H.264/AVC, AAC-LC Image quality

Normal Good Excellent

Profile Baseline Baseline Baseline

Level 3 3 3

Resolution 16:9 428×240 428×240 720×404

4:3 320×240 320×240 640×480

Bitrate

(kbps)

Video 200 500 1,500

Audio 48 96 192

Total 248 596 1,692

Video Frame rate 20 20 29.97

Audio

Sampling frequency

(KHz) 44.1 44.1 48

Stereo/Monaural Monaural Stereo Stereo

As the models for 2014 summer or later support H.265/HEVC, d anime Store will

expand its content lineup supporting H.265/HEVC. The content specifications for

H.265/HEVC have been determined in light of the concepts above to reduce the amount

of data and achieve “high-speed download.” The same frame rates are used for all the

levels of normal, good, and excellent because verification results showed that higher

frame rates had little impact on the image quality. Based on the concepts above and the

characteristics of anime content, the Store adopts parameter specifications different

from those shown in 5.1.2.

The following table shows video specifications of d anime store for H.265/HEVC.


- 40 -

Table 6-4 Video specifications for H.265/HEVC (d anime store)

H.265/HEVC, AAC-LC Image quality

Normal Good Excellent

Profile Main Main Main

Level 3 3 3.1

Tier Main Main Main

Resolution 16:9 428×240 428×240 852×480*

4:3 320×240 320×240 640×480

Bitrate

(kbps)

Video 100* 250* 700*

Audio 48 96 192

Total 148 346 892

Video Frame rate 29.97* 29.97* 29.97

Audio

Sampling frequency

(KHz) 44.1 44.1 48

Stereo/Monaural Monaural Stereo Stereo

*Different from H.264/AVC

6.5.2. File specifications for HLS technology

“d anime store” uses HLS for video streaming for iOS in accordance with the rules of

Apple Inc. The Store delivers video as a package of four files, which includes an

audio-only file according to the rules of Apple Inc. in addition to the three video files

shown in Table 6-3. The rules say that the size of an audio-only file “should never exceed

64 kbps even for a moment,” the Store encodes the audio data with an average rate of 32

kbps so that it will not exceed the maximum rate of 64kbps at any time. This is because

the file has been generated with VBR (Variable Bit Rate) due to such reasons as

encoding and software-related work, although generating a 64-kbps file with CBR

(Constant Bit Rate) may seem more reasonable.

The m3u8 file that integrates all the streams lists them in the order of excellent, good,

normal, and audio only. This arrangement has been made to accommodate customer

requests that they “want to enjoy anime with image quality as high as possible.”


- 41 -

Figure 6-1 File structure for HLS (d anime store Excellent)

On the other hand, some customers were asking for a reduction in the volume of LTE

communication and a capability to specify service quality by themselves. NTT

DOCOMO altered the Store mechanism in April 2014 so that customers can set the

highest image quality level by themselves.

・ Excellent: (Excellent--> Good -- > Normal -- > Audio only)

・ Good : (Good -- > Normal -- > Audio only)

・ Normal : (Normal -- > Audio only)

6.6. 【Information】Introduction of tools

This section introduces some major tools that can be used to achieve the measures

described in Section 5.3. Please note that the links shown below may be subject to

change. Also, please be advised to use any of the tools in accordance with their terms of

use or licenses specified by their respective owners. NTT DOCOMO assumes no

responsibility for any damages, troubles, or other consequences resulting from the use

of the tools.

Still picture volume reduction tool:

modpagespeed: https://code.google.com/p/modpagespeed/

Smush.it: http://www.smushit.com/ysmush.it/

Web page improvement tools:

PageSpeed Insights: https://developers.google.com/speed/pagespeed/insights/

Yslow: http://developer.yahoo.com/yslow/

m3u8

動画（ 32K）

※ 音声のみ

m3u8

動画（普通）

m3u8

動画（）

m3u8

動画（すごくきれい）

m3u8

m3u8

Video (32k)

*Audio only

m3u8

(Normal)

Video

m3u8

Video

m3u8

Video

m3u8(Integrated)

(Excellent)(Good)


- 42 -

Acknowledgements

NTT DOCOMO would like to extend our deepest appreciation to J-Stream Inc.,

DWANGO Co., Ltd., Forecast Communications Inc., and NTT Plala Inc. for their

valuable insights provided during the creation of this document.

NTT DOCOMO is also grateful to NTT’s Network Technology laboratories, Service

Evolution Laboratories, and Media Intelligence Laboratories for their technical

assistance provided for us in preparing this document.

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